Surface-mounted resistor and substrate for mounting the same thereon

ABSTRACT

A surface-mounted resistor includes a flat-type base member having a first surface, a second surface, and a lateral surface. Each of the first and second surfaces has a rectangular shape. The surface-mounted resistor also includes a resistance element formed on the first surface; a pair of internal electrodes formed on both ends of the resistance element by being partially superposed with the resistance element; and a pair of external electrodes. Each of the external electrodes has a first bended portion having an L-shape formed by an internal electrode connection portion and a lateral portion, and a second bended portion having an L-shape formed by the lateral portion and a substrate connection portion. The internal electrode and the internal electrode connection portion are fixed to each other through a conductive fixation material, and a position of the base member is biased in a thickness direction toward the first bended portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of Japanese PatentApplication No. 2010-113779, filed on May 18, 2010, and Japanese PatentApplication No. 2011-065383, filed on Mar. 24, 2011, the entire contentsof which are hereby incorporated by reference.

TECHNICAL FIELD

Embodiments described herein relate to a surface-mounted resistor to bemounted on a printed substrate and the like, and a surface-mountedsubstrate for mounting the surface-mounted resistor thereon.

BACKGROUND

A surface-mounted resistor to be mounted on a surface-mounted substrateis generally used in, e.g., a vehicle. For example, Patent Document 1(Japanese Laid-Open Patent Publication No. (Hei) 7-201507) discloses achip resistor that has been proposed by the applicants of the presentdisclosure. As described in paragraph [0002] of Patent Document 1,vehicle electronic components are required to be capable of withstandinghigh voltages.

Patent Document 2 (Japanese Laid-Open Patent Publication No. (Hei)8-203701) discloses a chip-type fixed resistor used in a circuit such asa vehicle electronic component, to which a surge voltage is applied.More particularly, Patent Document 2 provides a chip-type fixed resistorhaving an improved surge withstanding property that suppresses dischargebetween electrodes. As shown in FIG. 2 of Patent Document 2, a pair oflateral electrodes covering a part of an upper surface electrode isprovided on a lateral surface of an alumina substrate.

Patent Document 3 (Japanese Laid-Open Patent Publication No. (Hei)11-68284) discloses a surface-mounted electronic component forrestraining fatigue, cracks, and breaks due to thermal stress that isgenerated at a solder fillet tip and a solder joint. For such property,recesses and protrusions are provided on an electrode that is disposedon both lateral surfaces of the surface-mounted electronic component. Inthis way, stress concentration may be alleviated.

Patent Document 4 (Japanese Laid-Open Patent Publication No. (Hei)7-230901), which has been filed by the applicants of the presentdisclosure, discloses a surface-mounted type electronic component foralleviating impact applied to a lead terminal in the process of beingmounted on a surface-mounted substrate. For this purpose, thesurface-mounted type electronic component is mounted on thesurface-mounted substrate by interposing a buffer member therebetween.

Patent Document 5 (Japanese Laid-Open Patent Publication No. (Hei)8-115803) discloses a chip resistance component that issurface-mountable on a printed wiring board. More particularly, PatentDocument 5 describes that a soldering section of the chip resistancecomponent is not cracked or peeled upon being mounted. As described inparagraph [0007] and shown in FIGS. 1(a) through 1(c) of Patent Document5, a hole 16 is provided in a vertical portion 15a so as to strengthen aconnection between an external electrode 15 and a resistance element 10.Also, with reference to FIG. 5 of Patent Document 5, an externalelectrode 45 is made up of a vertical portion 45a, a lower portion 45b,a lateral portion 45c, and an upper portion 45d. As shown in FIG. 5 ofPatent Document 5, the external electrode 45 is attached on both ends ofthe resistance element 10 by burying the lateral portion 45c through aninsert molding. Further, surfaces of the vertical portion 45a, the lowerportion 45b, and the upper portion 45d are aligned on the same level asa surface of the resistance element 10, thereby being exposed to theoutside.

Patent Document 6 (Japanese Laid-Open Patent Publication No.2001-297942) discloses an electronic component provided with terminals.The electronic component has durability against stress applied from acircuit board in the process of being mounted on the circuit board bysoldering. Also, the terminals of the electronic component areconfigured in a flat structure (i.e., a low height structure) thatrestrains problems caused by the insufficiency and suction of a solderin the mounting process.

Patent Document 7 (Japanese Laid-Open Patent Publication No.2002-325302) discloses an apparatus and a method for accuratelydetecting an electric leakage occurring in a power supply that supplieselectric power to a motor used in an electric motor vehicle such as ahybrid car, an electric automobile, and the like. As described inparagraph [0002] of Patent Document 7, an output voltage of the powersupply employed in the electric motor vehicle is significantly high,e.g., 200 Volts (V) or more, such that an electric leakage in the powersupply may cause significant damage. To address this problem, for thesafety in a vehicle electronic system, the power supply should not bedirectly grounded and a leakage resistance should be detected so as toprevent the electric leakage. The leakage resistance refers to aresistance between the power supply and ground. Therefore, this leakageresistance may be detected by connecting the power supply to groundthrough a ground resistor of an electric leakage detection circuit.Considering the above, the ground resistor is required to have as largea resistance value as possible so as to prevent the risk of electricalshocks.

FIG. 11 shows a cross-sectional view illustrating a configuration of asurface-mounted resistor that is mounted on a surface-mounted substrate.A surface-mounted resistor 900 includes a flat-type base member 902, aresistance element 904, a protective film 906, a pair of upperelectrodes 908, a pair of lateral electrodes 910, and a pair of lowerelectrodes 912.

The lateral electrodes 910 and the lower electrodes 912 of thesurface-mounted resistor 900 are mounted on pads 918 of asurface-mounted substrate 916 by interposing solder fillets 920therebetween.

Referring to FIG. 12, a partial schematic cross-sectional viewillustrating a crack generated in the solder fillet 920 when thesurface-mounted resistor 900 (as shown in FIG. 11) is being mounted onthe surface-mounted substrate 916 is shown. The material of theflat-type base member 902 such as alumina has a different coefficient oflinear thermal expansion from the material of the surface-mountedsubstrate 916 (serving as an insulation substrate) such as glass epoxy.For this reason, repetitive variations in the temperature in the abovestructure, where the surface-mounted resistor 900 is mounted on thesurface-mounted substrate 916, may cause a shear force to be applied tothe solder fillet 920, which in turn causes a crack K thereon.

FIG. 13 shows a schematic cross-sectional view illustrating anelectronic component with a pair of L-shaped terminals, which is mountedon a surface-mounted substrate. The electronic component shown in FIG.13 is a partial variation of the electronic component having electrodesshown in FIG. 9 of Patent Document 6. An electronic component 950 havinga pair of L-shaped terminals is provided with an electronic element 952,a pair of internal electrodes 954, a pair of conductive resins 956, anda pair of external electrodes 958.

Each of the external electrodes 958 is provided with a stressalleviation portion 958 a. The electronic component 950 is mounted on aninsulation substrate 962 by interposing solder fillets 960 therebetween.

The electronic component 950 shown in FIG. 13 is provided with theelectronic element 952 and the pair of internal electrodes 954. Theelectronic element 952 is configured to be mounted on the insulationsubstrate 962 through the pair of external electrodes 958, such that thestress alleviation portions 958 a alleviate shear force applied to thesolder fillets 960, thereby preventing the generation of cracks.

The external electrodes 958 and the internal electrodes 954 are fixed toeach other by the conductive resins 956 in a direction perpendicular tothe insulation substrate 962. However, in this structure, if theelectronic component 950 having these electrodes is configured in a flatstructure, it may be difficult to secure a large fixation area in avertical direction. Therefore, there may be a problem that the fixationarea between the external electrode 958 and the internal electrode 954becomes insufficient.

Also, the movement of the stress alleviation portion 958 a is limited bythe solder fillet 960 formed along the external electrode 958, such thatthe shear force possibly being applied to the solder fillet 960 may notbe sufficiently absorbed by the stress alleviation portion 958 a.

Patent Document 1 describes the object of suppressing the deteriorationof a surge voltage withstanding property. However, Patent Document 1merely discloses the structural feature of a chip resistor while itneither suggests nor teaches mounting the chip resistor on thesurface-mounted substrate.

Patent Document 2 proposes substantially the same object as PatentDocument 1, for suppressing the deterioration of a surge voltagewithstanding property. Therefore, Patent Document 2 suggests a roundingtreatment on angled portions of both ends of electrodes of the chipresistor. However, Patent Document 2 neither suggests nor teachespossible problems that may be caused during a chip resistor mountingprocess, and countermeasures for such problems.

Patent Document 3 discloses the surface-mounted electronic component andconsiders problems such as fatigue, cracks, and breaks due to thermalstress generated at the solder fillet tip and the solder joint. Forovercoming the problems, Patent Document 3 suggests that the recessesand protrusions should be provided on the electrodes so as to absorbstresses. Unfortunately, this approach may cause another problem thatsuch electrode structure requires a more complicated manufacturingprocess resulting in a high manufacturing cost.

Patent Document 4 considers stress that is generated on the electroniccomponent in the process of being mounted on the surface-mountedsubstrate. For alleviating such stress, Patent Document 4 discloses thatthe buffer member is formed between a lower surface of the electroniccomponent and the surface-mounted substrate. As described in PatentDocument 4, a resin material such as an expanded urethane, a siliconeresin and the like, and a rubber material such as a silicone rubber areused as the buffer member. However, in order to precisely control athickness and an application range of the buffer member, a morecomplicated manufacturing process and apparatus is necessary, whichincreases manufacturing cost. Therefore, such approach may not bepreferable.

Patent Document 5 discloses the chip resistor component that issurface-mountable on a printed wiring board. As shown in FIG. 5 ofPatent Document 5, the external electrode 45 may be similar in shape toan E-shaped external electrode in accordance with one embodiment of thepresent disclosure. However, the external electrode 45 is configured tobe buried through the insert molding, which is structurally differentfrom the external electrode of the present disclosure. Such differencewill be apparent from the following descriptions.

Patent Document 6 considers alleviating stress due to thermal expansionand contraction in the circuit substrate. However, as described inPatent Document 6, the external electrodes are disposed on both lateralsurfaces of the electronic component.

Patent Document 7 discloses, in paragraph [0018], that the risk ofelectric shocks is decreased by employing a voltage-dividing resistor inthe electric leakage detection apparatus, the voltage-dividing resistorhaving a large resistance value, for example, 1 to 10 Mega Ohms.However, Patent Document 7 neither suggests nor teaches the structure ofa surface-mounted resistor having a large resistance value.

SUMMARY

It is, therefore, an object of some embodiments of the presentdisclosure to provide a surface-mounted resistor and a surface-mountedsubstrate, which can alleviate stress due to thermal expansion andcontraction made in the surface-mounted substrate when thesurface-mounted resistor is mounted thereon, and to improve suchalleviation ability against stress.

According to a first aspect of the present disclosure, a surface-mountedresistor comprises a flat-type base member having a first main surface,a second main surface, and lateral surfaces, each of the first mainsurface and the second main surface having a long side and a short side;and a resistance element formed on the first main surface of theflat-type base member. A pair of internal electrodes is integrallyformed with the resistance element to be provided on both ends thereof.Also, each of a pair of external electrodes has a first bended portion,a second bended portion, an internal electrode connection portion, alateral portion, and a substrate connection portion, wherein the firstbended portion is configured to have an L-shape by a combination of theinternal electrode connection portion and the lateral portion, and thesecond bended portion is configured to have an L-shape by a combinationof the lateral portion and the substrate connection portion. Theinternal electrode and the internal electrode connection are fixed toeach other through a conductive connection material. A position of theflat-type base member in its thickness direction is deviated toward thefirst bended portion.

In the surface-mounted resistor according to the first aspect of thepresent disclosure, the flat-type base member having the resistanceelement formed thereon is spaced apart from the substrate connectionportion provided on the second bended portion and thus, a space portionmay be formed between the second main surface of the flat-type basemember and the surface-mounted substrate. Through the space portion,stress due to thermal expansion and contraction applied from thesurface-mounted substrate to the flat-type base member may bealleviated.

In a second aspect of the surface-mounted resistor according to thefirst aspect, each of the pair of external electrodes is configured tohave a Z-shape by a combination of the first bended portion and thesecond bended portion, wherein an upper portion of the Z-shaped externalelectrode is configured as the internal electrode connection portion, alower portion of the Z-shaped external electrode is configured as thesubstrate connection portion, a connection portion for connecting theupper portion and the lower portion of the Z-shaped external electrodeis configured as the lateral portion. The substrate connection portionis configured to be protruded toward the outer side away from an end ofthe long side of the flat-type base member. With such configuration, thesubstrate connection portion being fixed on the surface-mountedsubstrate is bent toward the outer side to be protruded from theflat-type base member. Therefore, a connection state between thesubstrate connection portion and the surface-mounted substrate can beeasily checked through the eyes of a manufacturer.

In a third aspect of the surface-mounted resistor according to the firstaspect, the pair of lateral portions and the second main surface of theflat-type base member are partially fixed to each other through anadhesive. With such configuration, the flat-type base member is fixed atthe two internal electrode connection portions of the pair of externalelectrodes and two points on the second main surface, such that aconnection strength of the flat-type base member may be increased.

In a fourth aspect of the surface-mounted resistor according to thefirst aspect, each of the pair of external electrodes is configured tohave an E-shape including an upper spatial region and a lower spatialregion, which are divided by a middle portion being provided between thefirst bended portion and the second bended portion. The flat-type basemember is disposed in the upper spatial region of the E-shaped externalelectrode, whereas the lower spatial region of the E-shaped externalelectrode is used as a space portion.

With such configuration, the flat-type base member having the resistanceelement formed thereon is disposed in the upper spatial region of theE-shaped external electrode. The lower spatial region is used as thespace portion which may alleviate and absorb thermal stress andmechanical vibration, which are applied from the surface-mountedsubstrate to the resistance element.

In a fifth aspect of the surface-mounted resistor according to thefourth aspect, a section of the middle portion configuring a part of theE-shape and the second main surface of the flat-type base member arefixed to each other through an adhesive. With such configuration, thesecond main surface of the flat-type base member is further fixed to themiddle portion that is provided on a middle of the E-shaped externalelectrode. Therefore, a connection strength between the flat-type basemember and the pair of external electrodes may be more increased.

In accordance with the present disclosure, a surface-mounted substratehaving the surface-mounted resistor formed thereon is provided. Thesurface-mounted substrate includes a first adhesive surface and a secondadhesive surface, which are configured to be connected to both ends ofthe surface-mounted resistor. A shortest distance between the pair oflateral portions of the surface-mounted resistor is less than a shortestdistance between opposite facing ends of the first and second adhesivesurfaces. With such configuration, even when the two substrateconnection portions of the pair of external electrodes are fixed to thefirst and second adhesive surfaces through the conductive fixationmaterial such as a solder or the like, it may restrain the spread of asolder wetting up to the space portion that is formed between the secondmain surface of the flat-type base member and the surface-mountedsubstrate. As a result, the space portion may serve as a stressalleviation portion for alleviating stress due to thermal expansion andcontraction applied from the surface-mounted substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a surface-mounted resistor inaccordance with a first embodiment of the present disclosure.

FIG. 2 is a lateral view showing the surface-mounted resistor inaccordance with the first embodiment of the present disclosure.

FIG. 3A is a lateral view showing one modification example of the firstembodiment according to the present disclosure.

FIG. 3B is a lateral view showing another modification example of thefirst embodiment according to the present disclosure.

FIG. 4 is a diagram showing a connection between an internal electrodeand an external electrode of the surface-mounted resistor shown in FIG.2.

FIG. 5A is a diagram showing one example of a connection between theexternal electrode of the surface-mounted resistor and an adhesivesurface of a surface-mounted substrate in accordance with the firstembodiment of the present disclosure, where the adhesive surface isdisposed at inner position than the external electrode.

FIG. 5B is a diagram showing another example of connection between theexternal electrode of the surface-mounted resistor and the adhesivesurface of the surface-mounted substrate in accordance with the firstembodiment of the present disclosure, where the adhesive surface isdisposed at outer position than the external electrode.

FIG. 6 is a plan view showing a surface-mounted resistor in accordancewith a second embodiment of the present disclosure.

FIG. 7 is a lateral cross-sectional view showing the surface-mountedresistor shown in FIG. 6.

FIG. 8A is a perspective view showing a surface-mounted resistor inaccordance with a third embodiment of the present disclosure.

FIG. 8B shows a modification example of the third embodiment accordingto the present disclosure.

FIG. 9 is a perspective view showing a surface-mounted resistor inaccordance with a fourth embodiment of the present disclosure.

FIG. 10 is a lateral cross-sectional view showing the surface-mountedresistor shown in FIG. 9.

FIG. 11 shows a lateral cross-section view for explaining a conventionalsurface-mounted resistor.

FIG. 12 shows a diagram for explaining a state when a crack is generatedon a soldering portion of the conventional surface-mounted resistorshown in FIG. 11.

FIG. 13 shows another example of the conventional surface-mountedresistor including a partial modification of an electric element havingan L-shaped terminal shown in FIG. 10 of Patent Document 6.

DETAILED DESCRIPTION First Embodiment

FIG. 1 shows a perspective view of a surface-mounted resistor inaccordance with a first embodiment of the present disclosure. Asurface-mounted resistor 100 includes a flat-type base member 102, apair of internal electrodes 104, a resistance element 106, a protectivelayer 107, conductive fixation materials 108, and a pair of externalelectrodes 110. The resistance element 106 is disposed under theprotective layer 107. The resistance element 106 is not shown in FIG. 1.Further, even though not shown in FIG. 1, a plating treatment may beperformed on the pair of external electrodes 110 and the pair ofinternal electrodes 104. The conductive fixation materials 108 mayinclude solder, paste, or the like.

Each of the pair of external electrodes 110 includes an internalelectrode connection portion 112, a lateral portion 114, and a substrateconnection portion 116. Each of the pair of external electrodes 110includes an L-shaped first bended portion 110 a formed by a combinationof the internal electrode connection portion 112 and the lateral portion114, and an L-shaped second bended portion 110 b formed by a combinationof the lateral portion 114 and the substrate connection portion 116.Each of the pair of external electrodes 110 may have an approximate Zshape. For example, the external electrode 110 is bent at the secondbended portion 110 b in a direction away from the flat-type base member102 (i.e., in an outer direction) but not in a direction toward theflat-type base member 102 (i.e., in an inner direction). The resistanceelement 106 is formed on a first main surface of the flat-type basemember 102. The flat-type base member 102 and the resistance element 106may be integrally combined.

A space enclosed by the flat-type base member 102 and the externalelectrodes 110 is referred to as a space portion 110 s. A height H1 ofthe external electrode 110 is set so as to make the space portion 110 sto have a predetermined space volume. The height H1 of the externalelectrode 10 may be adjusted depending on a thickness of the flat-typebase member 102. In the present disclosure, the space portion 110 s isprepared to prevent the resistance element 106 formed on the flat-typebase member 102 from being affected by stress due to thermal expansionand contraction of a surface-mounted substrate.

In an exemplary embodiment, the height H1 of the external electrodes 110may be 2.0 mm, a width W1 of the external electrodes 110 may be 3.2 mm,a length L3 between ends of the pair of external electrodes 110 may be10.4 mm, a length L5 between inner lateral surfaces of the pair ofexternal electrodes 110 may be 8.4 mm, and a thickness t1 of theexternal electrodes 110 may be 0.1 mm, for example.

FIG. 2 illustrates a lateral view of the surface-mounted resistor 100shown in FIG. 1. In FIG. 2, the surface-mounted resistor 100 is mountedon the surface-mounted substrate. In FIG. 2, components or portionscorresponding to those of FIG. 1 have the same reference numerals. Thesurface-mounted resistor 100, as shown in FIG. 1, includes the flat-typebase member 102, the pair of internal electrodes 104, the resistanceelement 106, the protective layer 107, the conductive fixation materials108, and the pair of external electrodes 110.

The flat-type base member 102 is made of a relatively high purityalumina, e.g., having a purity of 92% or 96%. The alumina has excellentmechanical strength, thermal conductivity, and insulation properties. L1indicates a length of a long side edge of the flat-type base member 102in FIG. 2.

The pair of internal electrodes 104 is formed on a first main surface102 a of the flat-type base member 102. The pair of internal electrodes104 is made of a silver-palladium baked alloy. The internal electrode104 may be formed extending to an end of the first main surface 102 a ofthe flat-type base member 102 shown in FIG. 2 (for example, an outerlateral surface of the internal electrode 104 may be formed extending toa lateral surface 102 s of the flat-type base member 102).Alternatively, the internal electrode 104 may be formed extending to aposition, which is spaced a predetermined distance from the end side(the position of the lateral surface 102 s) towards the inner side ofthe first main surface 201 a. The resistance element 106 is formed onthe first main surface 102 a of the flat-type base member 102. Theresistance element 106 may be partially superposed with the pair ofinternal electrodes 104. FIG. 2 shows an example where both end portionsof the resistance element 106 are placed over the pair of the internalelectrodes 104. Alternatively, the pair of internal electrodes 104 maybe placed over left and right portions of the resistance element 106.The resistance element 106 is made of a mixed material including, e.g.,ruthenium oxide (RuO₂) and glass. A resistance value of the resistanceelement 106 may be controlled by changing a ratio of mixing theruthenium oxide (RuO₂) and the glass. A rate of containing the glass maybe increased to obtain a higher resistance value, whereas a rate ofcontaining the ruthenium oxide (RuO₂) may be increased to obtain a lowerresistance value. It is known that the ruthenium oxide (RuO₂) has anexcellent weather resistant property, i.e., a property of resistingdeterioration such as deformation, discoloration and degradation.

The resistance element 106 is covered with the protective layer 107. Theprotective layer 107 may separate and protect the resistance element 106from contacting the air. Also, the protective layer 107 may protect theresistance element 106 from corrosion caused by a plating solution usedin a plating process to be performed on the pair of internal electrodes104 and the pair of external electrodes 110.

The resistance element 106 is configured to have a rectangular shape. Adistance between two conductive regions (i.e., the both lateral ends) ofthe resistance element 106, i.e., a clearance distance is indicated byL2 in the drawing. Also, the length L2 corresponds to a distance betweenthe pair of internal electrodes 104. Further, a creepage distanceindicates the shortest distance along a surface of an insulatingmaterial between the two conductive regions. However, in the presentembodiment according to the present disclosure, the creepage distanceand the clearance distance are substantially the same as each other.Furthermore, respective dimensions of the creepage distance and theclearance distance and a difference between the respective dimensionsmay vary depending on a structure of the surface mounted resistor 100

The length L2 may vary depending on a withstanding voltage required forthe resistance element 106. For example, the applicant found that if awithstanding voltage is, e.g., 1.5 kilovolt (kV), the length L2 isrequired to be 5.2 mm or more. Therefore, in the present embodimentaccording to the present disclosure, the length L2 is set to be, e.g.,5.3 mm that is slightly greater than 5.2 mm. A length L1 of the longside of the flat-type base member 102 is set to be, e.g., 7.9 mm bytaking into account the length L2 and dimensions of the pair of internalelectrodes 104. A length of the short side of the flat-type base member102 is set to be, e.g., 4 mm. As described above, the length L3 betweenthe ends of the pair of substrate connection portions 116 is set to be,e.g., 10.4 mm.

The protective layer 107 is made of glass and epoxy resin. For example,the resistance element 106 is first covered with the glass, and then theglass just above the resistance element 106 is covered with first andsecond epoxy resins in turn, thereby making the protective layer 107 tohave a three-film lamination structure.

The internal electrode 104 is connected to the external electrode 110 byinterposing the conductive connection material 108 therebetween. Theconductive connection material 108 may include a solder paste or aconductive resin. For example, the conductive connection material 108shown in FIG. 2 may include the solder paste.

As described above, each of the pair of external electrodes 110 isprovided with the internal electrode connection portion 112 that isconnected to the internal electrode 104 by interposing the conductiveconnection material 108 therebetween, the lateral portion 114, and thesubstrate connection portion 116. The internal electrode connectionportion 112, the lateral portion 114, and the substrate connectionportion 116 are integrally formed using the same material. The internalelectrode connection portion 112 positioned on an upper side of theexternal electrode 110 and the lateral portion 114 are combined to formthe L-shaped first bended portion 110 a. In FIG. 2, an angle r1 of thefirst bended portion 110 a is shown to be a substantially right angle.Alternatively, in some embodiments, the angle r1 may be set to be anacute angle or an obtuse angle. However, when the angle r1 is set to bean acute angle or an obtuse angle, the acute angle or the obtuse anglemay be set not to deviate significantly from 90 degrees. Specifically,if the angle r1 is set to be an acute angle of, e.g., 60 degrees orless, a space (or range) for mounting the surface-mounted resistor 102and the pair of external electrodes 110 may be limited. Therefore, theangle r1 may be set to be in the range of 70 to 120 degrees, morespecifically, in the range of 80 to 110 degrees.

The lateral portion 114 and the substrate connection portion 116 arecombined to form the L-shaped second bended portion 110 b. The externalelectrode is bent in a direction away from the flat-type base member 102(i.e., in an outside direction), but not in a direction toward the innerside thereof, to form the second bended portion 110 b. With suchconfiguration, the two substrate connection portions 116 can be easilyadhered to a first adhesive surface 122 a and a second adhesive surface122 b, respectively. Also, this facilitates checking an adhesion statusbetween the two substrate connection portions 116 and the first andsecond adhesive surfaces 122 a and 122 b, with the eyes of amanufacturer.

In FIG. 2, an angle r2 of the second bended portion 110 b is shown as asubstantially right angle. Alternatively, in some embodiments, similarto the angle r1, the angle r2 may be set to be an acute angle or anobtuse angle. Since the second bended portion 110 b is integrally formedwith the first bended portion 110 a, the angle r2 may be set to besubstantially the same as the angle r1. For example, the angle r2 may beset to be in the range of 70 to 120 degrees, more specifically, in therange of 80 to 110 degrees.

As described above, each of the pair of external electrodes 110 is madeup with a combination of the first L-shaped bended portion 110 a and thesecond L-shaped bended portion 110 b. Therefore, if the angles r1 and r2are set to be acute angles, respectively, each of the pair of externalelectrodes 110 according to the first embodiment of the presentdisclosure has a Z-shape.

An inner lateral surface 114 a of the lateral portion 114 and thelateral surface 102 s of the flat-type base member 102 are spaced apartfrom each other by a distance L4, instead of being in contact with eachother. This configuration may prevent the inner lateral surface 114 aand the lateral surface 102 s from being damaged by contact therebetweeneven when the angles r1 and r2 of the first and second bended portions110 a and 110 b of the external electrode 110 are set to be acuteangles. The distance L4 is set to be, e.g., 0.25 mm.

The length L5 between the inner lateral surfaces 114 a of the pair ofexternal electrodes 110 is set to be shorter than a length L6 betweenthe opposite facing ends of the first and second adhesive surfaces 122 aand 122 b. That is, the first and second adhesive surfaces 122 a and 122b are disposed at positions spaced farther from the space portion 110 sthan the inner lateral surfaces 114 a of the external electrode 110.This may prevent a problem related to the space volume decrease of thespace portion 110 s, which is caused by any protrusions from solders 118toward the space portion 110 s.

The height H1 of the external electrode 110 represents a distance fromthe first bended portion 110 a to the second bended portion 110 b. Aheight H2 denotes a thickness of a main body of the surface-mountedresistor 100. A height H3 indicates a distance from the first bendedportion 110 a to a second main surface 102 b of the flat-type basemember 102. A height H4 of the space portion 110 s is the same as avalue obtained by subtracting the height H3 from the height H1. Theheight H2 is generally predetermined according to a structure of theexternal electrode 110. Therefore, a space volume of the space portion110 s is defined depending on the height H1. In order to allow thesurface-mounted resistor 100 to be more flat, the height H1 of theexternal electrode 110 may not be increased. However, in some cases moreweight is given to securing more area for space portion 110 s ratherthan having a flatter flat structure, thereby preventing or alleviatingstress due to thermal expansion and contraction applied from thesurface-mounted substrate 120 to the surface-mounted resistor 100.

For securing the space volume of the space portion 110 s in apredetermined dimension, the applicant implemented a prototype of thesurface-mounted resistor 100 according to the present disclosure withthe following dimensions: the height H1 is set to be 2.0 mm; the heightH2 is set to be 0.48 mm; the height H3 is set to be 0.58 mm; the heightH4 is set to be 1.42 mm; the length L1 is set to be 7.9 mm; the lengthL2 is set to be 5.3 mm; the length L3 is set to be 10.4 mm; the lengthL4 is set to be 0.25 mm; the length L5 is set to be 8.4 mm; and thelength L6 is set to be 8.5 mm. Such configuration suggests that aposition of the flat-type base member 102 in the thickness direction issignificantly biased toward the first bended portion 110 a. That is, theposition of the flat-type base member 102 is located significantly faraway from the second bended portion 110 b so as to be biased toward thefirst bended portion 110 a. This configuration provides the spaceportion 110 s between the second main surface 102 b of the flat-typebase member 102 and a main surface 120 a of the surface-mountedsubstrate 120 when mounting the surface-mounted resistor 100 on thesurface-mounted substrate 120.

Also, the length L1 of the flat-type base member 102 corresponds to alength of a typical chip resistor. As well known in the related art, thelength L1 of the chip resistor may have a certain limitation. Forexample, if the length L1 of the chip resistor exceeds 3.2 mm, cracksare likely to form on the chip resistor. For this reason, inmanufacturing the chip resistor, the length L1 may be generally limitedto be 3.2 mm or less. On the contrary, in accordance with the presentdisclosure, for improving a voltage withstanding property, the length L1of the flat-type base member 102 is set to be 7.9 mm, about 2.5 timesgreater than 3.2 mm. Also, for improving a crack resistant property, thespace portion 110 s is provided. Therefore, with such configuration ofthe present disclosure, both the voltage withstanding property and thecrack resistant property can be obtained.

In order to verify the dimension of the space portion 110 s, a spacevolume ratio Va may be calculated, wherein the space volume ratio Varepresents a ratio of the volume of the space portion 110 s to theentire volume of the surface-mounted resistor 100. Assuming that thesurface-mounted resistor 100 shown in FIGS. 1 and 2 is a substantiallyrectangular object, a space volume ratio Va is approximately representedas Va=H4/H1. Since the height H1 denotes a distance between the firstbended portion 110 a and the second bended portion 110 b, it mayrepresent the entire volume of the surface-mounted resistor 100.Further, since the height H4 denotes a height of the space portion 110s, it may represent a volume of the space portion 110 s.

Therefore, the space volume ratio Va of the space portion 110 s may beapproximately represented as Va=H4/H1. For example, in the presentembodiment according to the present disclosure, the space volume ratioVa becomes 0.71 (Va=1.42 mm/2.0 mm). The more the space volume ratio Vais increased, the more the influence of thermal stress on thesurface-mounted resistor 100 applied from the surface-mounted substrate120 is decreased. Because there is a limitation in decreasing athickness, i.e., the height H1, of the surface-mounted resistor 100,giving weight to the space volume ratio Va causes an increase of theheight H1, which is contrary to realizing a flat structure. However,when a flat structure is not strongly needed, this may not raise anycritical issues. Consequently, the space volume ratio Va may be selectedin the range of 0.3 to 0.9 depending on the purpose of thesurface-mounted resistor 100. Alternatively, in some embodiments, thespace volume ratio Va may be more specifically set to be 0.5 to 0.8.

When the space volume ratio Va becomes zero, the flat-type base member102 is provided at an approximately middle position between the firstbended portion 110 a and the second bended portion 110 b. Thus, theposition of the flat-type base member 102 in the thickness direction isnot biased to either of the bended portions. As the space volume ratioVa increases from zero, the degree of bias in the thickness direction isincreased. Therefore, the space volume ratio Va also represents thedegree of bias of the flat-type base member 102.

FIG. 3A illustrates one modification example of the first embodimentshown in FIG. 2. In FIG. 3A, components or portions corresponding tothose shown in FIG. 2 have the same reference numerals. While thereference numerals shown in FIG. 2 may also be used in FIG. 3A, some ofthe reference numerals will be omitted for clarity of illustration. Themodification example shown in FIG. 3A is different from the firstembodiment of the present disclosure shown in FIG. 2 in that theflat-type base member 102 is turned upside down and attached to the pairof external electrodes 110. Specifically, the first embodiment shown inFIG. 2 discloses the flat-type base member 102 that is suspended fromthe two internal electrode connection portions 112 of the pair ofexternal electrodes 110 by interposing the conductive fixation materials108 therebetween. On the other hand, the modification example shown inFIG. 3A discloses the flat-type base member 102 that is placed over thetwo internal electrode connection portions 112 of the pair of externalelectrodes 110 by interposing the conductive fixation materials 108therebetween. Therefore, according to the first embodiment shown in FIG.2, the second main surface 102 b of the flat-type base member 102 islocated nearer to the second bended portion 110 b. On the contrary,according to the modification example shown in FIG. 3A, the second mainsurface 102 b of the flat-type base member 102 is located farther fromthe second bended portion 110 b.

In the modification example of the first embodiment shown in FIG. 3A,the flat-type base member 102 as a part of the surface-mounted resistor100 includes the first main surface 102 a and the second main surface102 b, each of which has a rectangular shape one side of which is longerthan the other side, and the lateral surfaces 102 s. On the first mainsurface 102 a of the flat-type base member 102, the resistance element106 having a longer side and a shorter side is formed. Near both ends ofthe long side of the resistance element 106, a pair of internalelectrodes 104 are foamed by being partially superposed with theresistance element 106. The first bended portion 110 a has an L-shapethat is formed by a combination of the internal electrode connectionportion 112 and the lateral portion 114. The second bended portion 110 bhas an L-shape that is formed by a combination of the lateral portion114 and the substrate connection portion 116. Each of the pair ofexternal electrodes 110 includes the first bended portion 110 a and thesecond bended portion 110 b. The pair of internal electrodes 104 and theinternal electrode connection portions 112 are fixed to each otherthrough the conductive fixation materials 108. A position of theflat-type base member 102 in the thickness direction is biased towardthe first bended portion 110 a that is furthermost positioned from thesecond bended portion 110 b in the external electrode 10.

Also, in the modification example shown in FIG. 3A, the flat-type basemember 102 is located at a position outside the space portion 110 s.This configuration of the modification example is different from thefirst embodiment shown in FIG. 2 where the flat-type base member 102provided with the resistance element 106 formed thereon is locatedinside the space portion 110 s. As shown in FIG. 3A, since the flat-typebase member 102 is located outside the space portion 110 s in themodification example, heat dissipation efficiency may be increased.Further, in the modification example, the flat-type base member 102 isplaced over the internal electrode connection portions 112, so that amechanical strength of the conductive fixation materials 108, which fixthe pair of internal electrodes 104 to the internal electrode connectionportions 112, is not strictly required in comparison with the firstsuspension-type embodiment shown in FIG. 2.

FIG. 3B shows another modification example of the first embodimentaccording to the present disclosure. This modification example isdifferent from the modification example shown in FIG. 3A in that thelateral surface 102 s of the flat-type base member 102 is fixed to theinternal electrode connection portion 112 through an adhesive 142 (aprotective material made of an insulation resin). With suchconfiguration, a fixation strength between the flat-type base member 102and the pair of external electrodes 110 may be further increased. Also,the protective material 142 is provided so as to cover the entiresurface of the conductive fixation material 108. In FIG. 3B, outer andinner sections of the protective material 142 covering the outside andinside of the conductive fixation material 108 are indicated byreference numerals 142 a and 142 b, respectively. With suchconfiguration, the conductive fixation materials 108 prevent exposure tothe air. The conductive fixation materials 108 are made of, e.g., Ag. Ifa voltage is applied to the conductive fixation materials 108 while itis in contact with moisture, migration may be generated. However, bycovering the conductive fixation materials 108 with the protectivematerial 142, the generation of such migration may be prevented. Inaddition, the conductive fixation materials 108 may be prevented frombeing sulfurized. A range of the protective material 142 for coveringthe conductive fixation material 108 may be in a minimum range. Forexample, as shown in FIG. 3B, the outer section 142 a of the protectivematerial 142 is provided to cover an area ranging from the lateralsurface 102 s of the flat-type base member 102 to an upper surface ofthe internal electrode connection portion 112. The outer section 142 adoes not surmount on the second main surface 102 b. The inner section142 b of the protective material 142 is provided to cover an end of theprotective layer 107 on the resistance element 106 and a part of a lowersurface of the internal electrode connection portion 112. The outersection 142 a of the protective material 142 may be configured not tocover the lateral portion 114 of the external electrode 110. Further,the inner section 142 b of the protective material 142 may be configurednot to cover the lateral portion 114 (the inner lateral surface 114 a)of the external electrode 110. The following is a description of thereason why the lateral portion 114 of the external electrode 110 shouldnot be covered with the protective material 142. When the lateralportion 114 is covered with the protective material 142 (142 a or 142b), a deformation of the lateral portion 114 is limited by theprotective material 142. As a result, it is difficult to sufficientlyabsorb a shear force generated due to the difference in coefficients oflinear thermal expansion between the flat-type base member 102 and theinsulation substrate 120 through a deformation of the lateral portion114. In addition, the protective material 142 covers the conductivefixation material 108 and the internal electrode 104 to prevent themfrom being exposed to air. Therefore, a sulfurization of the internalelectrode 104 is prevented. Alternatively, the protective material 142may be locally applied only on a part of the first main surface 102 a ofthe flat-type base member 102, but not the lateral surfaces 102 sthereof, so that the protective material 142 does not exist on thelateral surfaces 102 s. As the protective material 142, for example, anultraviolet (UV) curing adhesive having a property of being cured in ashort time may be used.

FIG. 4 illustrates an enlarged view of a circle A shown in FIG. 2. InFIG. 4, the vicinity of the internal electrode connection portion 112 ofthe external electrode 110 is enlarged. As described above, the externalelectrode 110 includes the internal electrode connection portion 112,the lateral portion 114, and the substrate connection portion 116. Theseportions are integrally formed using a same material. For example, aninner plating layer 112 b is provided on a base member 112 a made of acopper-nickel alloy, and an outer plating layer 112 c is provided on theinner plating layer 112 b. For example, the inner plating layer 112 bmainly contains nickel, whereas the outer plating layer 112 c mainlycontains tin.

A part of the inner electrode connection portion 112 is electricallyconnected to the internal electrode 104 through the conductive fixationmaterial 108 by interposing an internal electrode plating layer 104 atherebetween. The internal electrode 104 is made of, e.g.,silver-palladium or platinum. The internal electrode plating layer 104 ais configured in a double-layered structure of, e.g., a nickel platinglayer and a tin plating layer so as to prevent solder corrosion.

In FIG. 4, solder is used as the conductive fixation material 108 forfixing the internal electrode 104 to the internal electrode connectionportion 112. In this configuration, the internal electrode plating layer104 a, the inner plating layer 112 b, and the outer plating layer 112 care required for implementing proper electric conduction therebetween.Alternatively, the internal electrode 104 and the internal electrodeconnection portion 112 are fixed to each other through the conductivefixation material 108 made of, e.g., a conductive resin. In thisconfiguration, the conductive resin is coated and fixed to the internalelectrode 104 and the internal electrode connection portion 112, andthen the coated conductive resin is subject to a plating treatment. Inthis case, the internal electrode plating layer 104 a does not need tobe interposed between the conductive fixation material 108 and theinternal electrode 104. Further, the inner plating layer 112 b and theouter plating layer 112 c do not need to be disposed between theconductive fixation material 108 and the internal electrode connectionportion 112. As a result, the internal electrode 104 and the internalelectrode connection portion 112 are directly connected to each other.

As shown in FIG. 2, FIG. 3A, FIG. 3B, and FIG. 4, in the surface-mountedresistor 100 according to the first embodiment of the presentdisclosure, the resistance element 106 and the internal electrodeconnection portions 112 are electrically connected to each other throughthe pair of internal electrodes 104 that are provided on the first mainsurface 102 a of the flat-type base member 102. That is, for the purposeof facilitating manufacturing, the pair of internal electrodes 104 areprovided only on the first main surface 102 a of the flat-type basemember 102, but not on the lateral surfaces 102 s of the flat-type basemember 102. As such, a formation and manufacturing process of theinternal electrode 104 can be performed in a simpler manner and thus amanufacturing cost can be reduced.

Further, the internal electrode 104 is formed on the first main surface102 a of the flat-type base member 102 having a relatively wide area.With such configuration, a fixation area of the internal electrode 104can be extended, compared to when a fixation area on the lateral surface102 s of the flat-type base member 102 is provided. Therefore, afixation strength in the internal electrode 104 can be increased.

If the internal electrode 104 is provided on the first main surface 102a of the flat-type base member 102, a fixation area between the internalelectrode 104 and the internal electrode connection portion 112 isdetermined depending on an area of the internal electrode 104. On theother hand, if the internal electrode 104 is provided on the lateralsurface 102 s of the flat-type base member 102, a fixation area betweenthe internal electrode 104 and the internal electrode connection portion112 is determined depending on a thickness of the flat-type base member102. Assuming that a thickness of the flat-type base member 102 is setto be 0.48 mm, a side length of the internal electrode 104 is set to be0.96 mm, and a width W1 (shown in FIG. 1) of the external electrode 110is set to be 3.2 mm, if the internal electrode 104 is provided on thelateral surface 102 s of the flat-type base member 102, a fixation areabecomes 0.48 mm×3.2 mm=1.54 mm². Alternatively, if the internalelectrode 104 is provided on the first main surface 102 a of theflat-type base member 102, a fixation area becomes 0.96 mm×3.2 mm=3.07mm². As described above, by providing the internal electrode 104 on thefirst main surface 102 a of the flat-type base member 102, it ispossible to have a fixation area expanded approximately twice comparedto the case of providing the internal electrode 104 on the lateralsurface 102 s of the flat-type base member 102. If the internalelectrode 104 is provided on the first main surface 102 a of theflat-type base member 102, a fixation area may be set to be 1.2 timeslarger or greater, more specifically 1.5 times or greater than when theinternal electrode 104 is provided on the lateral surface 102 s of theflat-type base member 102.

In other words, one of the features of the present embodiment is that anarea of the external electrode 110 facing the internal electrode 104 isset to be wider than that of the external electrode 110 facing thelateral surface 102 s of the flat-type base member 102.

The resistance element 106 is formed on the first main surface 102 a ofthe flat-type base member 102. As described above, the resistanceelement 106 is made of a mixture powder of, e.g., ruthenium oxide (RuO₂)and glass. The mixture powder is mixed with an organic binder to form apaste. The paste is applied on the flat-type base member 102 through,e.g., a screen printing and baked at a temperature of 800 to 900 degreesCelsius, thereby forming a thick film of about 10 micrometer (μm)thickness.

The resistance element 106 is covered with the protective layer 107. Theprotective layer 107 is made of at least one of, e.g., glass and anepoxy resin. In some embodiments, the glass and the epoxy resin may belayered to form the protective layer 107. For example, glass is coatedon an upper surface of the resistance element 106, and then a firstepoxy resin layer and a second epoxy resin layer are sequentiallycovered thereon.

As shown in FIG. 4, the flat-type base member 102 with the resistanceelement 106 formed thereon is suspended from the internal electrodeconnection portion 112 of the external electrode 110 through theconductive fixation material 108.

FIG. 5A illustrates an enlarged view of a circle B shown in FIG. 2.Components or portions corresponding to those shown in FIG. 2 have thesame reference numerals. As described above, FIG. 4 shows an enlargedview of the vicinity of the internal electrode connection portion 112 ofthe external electrode 110, whereas FIG. 5A shows an enlarged view ofthe vicinity of the substrate connection portion 116, which serves asanother connection portion of the external electrode 110. On theexternal electrode 110, the inner plating layer 112 b mainly made ofnickel and the outer plating layer 112 c mainly made of tin are formed.

In the process of mounting the surface-mounted resistor 100 on thesurface-mounted substrate 120, the first adhesive surface 122 a isdisposed at an outer position than the inner lateral surface 114 a ofthe lateral portion 114, i.e., in a direction away from the flat-typebase member 102. As a result, the first adhesive surface 122 a isdisposed at a position away from the space portion 110 s. In this way,the solder 118 may not flow into the space portion 110 s where theflat-type base member 102 is disposed, such that a protrusion of thesolder 118 toward the space portion 110 s is prevented. This solderingstate is shown as reference numeral 118 x 1 in FIG. 5. With suchconfiguration, it is possible to prevent the contact of the solder 118with the flat-type base member 102, thereby restraining the thermaldeformation of the resistance element 106 and the reduction of the spaceportion 110 s. Further, by securing the space volume of the spaceportion 110 s with a predetermined dimension, thermal stress of theresistance element 106 applied from the surface-mounted substrate 120may be restrained. Similar to the first adhesive surface 122 a, thesecond adhesive surface 122 b shown in FIG. 2 may provide the sameeffects.

FIG. 5B illustrates another configuration of the circle B shown in FIG.2. Contrary to the example of the soldering state 118 x 1 shown in FIG.5A, the soldering state 118 x 2 shown in FIG. 5B may have some issues asexplained below. Specifically, FIG. 5B shows a schematic example inwhich the first adhesive surface 122 a provided on the surface-mountedsubstrate 120 is extended to a position that is closely located towardthe flat-type base member 102, i.e., toward the space portion 110 s,more than the inner lateral surface 114 a of the lateral portion 114. Inthe process of mounting the surface-mounted resistor 100 on thesurface-mounted substrate 120 with the above-described configuration, afillet of the solder 110 may be flown along the inner lateral surface114 a, which decreases the space volume of the space portion 110 s. As aresult, the resistance element 106 is readily affected by the thermalimpact and mechanical vibration from the surface-mounted substrate 120.Similar to the first adhesive surface 122 a, the second adhesive surface122 b shown in FIG. 2 may provide the same effects.

For solving the problems related to the configuration shown in FIG. 5B,the length L6 representing the shortest distance between the firstadhesive surface 122 a and the second adhesive surface 122 b may bedesigned to be greater than the length L5 between the inner lateralsurfaces 114 a of the pair of lateral portions 114 of thesurface-mounted resistor 100.

Second Embodiment

FIG. 6 shows a plan view of a second embodiment in accordance with thepresent disclosure. A surface-mounted resistor 100 includes a flat-typebase member 102, a pair of internal electrodes 104, a resistance element106, and a pair of external electrodes 110. Components or portionscorresponding to those shown in FIG. 1 and FIG. 2 have the samereference numerals. Also, in order to clarify the configuration of theresistance element 106, the protective layer 107 (shown in FIG. 2) isnot shown in FIG. 6. The protective layer 107 (not shown) is made of acombination of glass and epoxy. Each of the pair of external electrodes110 includes the internal electrode connection portion 112 and thesubstrate connection portion 116. Each of the pair of externalelectrodes 110 also has the lateral portion 114. However, the lateralportion 114 is not shown in the plan view of FIG. 6.

The substrate connection portions 116 are soldered on the first adhesivesurface 122 a and the second adhesive surface 122 b. The first adhesivesurface 122 a and the second adhesive surface 122 b are a part of wiringpatterns that are disposed on the surface-mounted substrate 120. Whenviewed in a direction x1, wiring ends 122 s of the first adhesivesurface 122 a and the second adhesive surface 122 b are disposed closerto a center 106 c of the resistance element 106 than the lateral surface102 s of the flat-type base member 102.

FIG. 7 illustrates a schematic lateral cross-sectional view of thesurface-mounted resistor 100 shown in FIG. 6. Components or portionscorresponding to those shown in FIG. 1, FIG. 2, and FIG. 6 have the samereference numerals. A major difference from the first embodiment shownin FIG. 2 is that the second main surface 102 b and the lateral surface102 s of the flat-type base member 102, and the inner lateral surface114 a of the lateral portion 114 of the external electrode 110 are fixedto each other through an adhesive 143. In this way, the flat-type basemember 102 is fixed to the external electrode 110 by interposing theconductive fixation material 108 between the internal electrode 104 andthe internal electrode connection portion 112 on the first main surface102 a, while the flat-type base member 102 is fixed to the externalelectrode 110 by using the adhesive 143 on the second main surface 102b. Therefore, an adhesive strength between the flat-type base member 102and the external electrode 114 may be further increased. Specifically,as shown in FIG. 7, the flat-type base member 102 is fixed to externalelectrode 110 at two opposing positions in the thickness direction suchthat the adhesive strength may be increased.

Depending on the height H2 of the main body of the surface-mountedresistor 100, the height H1 of the external electrode 110 defines theheight H4 from the second main surface 102 b of the flat-type basemember 102 to a bottom surface of the substrate connection portion 116.Further, in a similar manner, the height H1 defines a distance from thesecond main surface 102 b to the main surface 120 a of thesurface-mounted substrate 120. As a result, the space volume of thespace portion 110 s is approximately determined by the height H4. Whilethe height H5 from a bottom end of the adhesive 143 to the bottomsurface of the substrate connection portion 116 is determined based onthe height H4, the bottom end of the adhesive 143 may be disposed as faras possible away from the main surface 120 a of the surface-mountedsubstrate 120. In this way, a decrease of the space volume of the spaceportion 110 s may be restrained. For example, if the height H1 is set tobe 2.0 mm, the height H4 may be set to be 1/10 of the height H1 or more,more specifically, ½ the height H1 or more. As the space volume(Va=H4/H1) is decreased, it is difficult to set the height H4 to be 1/10the height H1 or more. In this case, the flat-type base member 102 andthe external electrode 110 may be fixed to each other by injecting theadhesive 143 into a gap between the lateral surface 102 s of theflat-type base member 102 and the inner lateral surface 114 a of theexternal electrode 110.

As the adhesive 143, a UV (ultraviolet) adhesive may be used, forexample. This UV adhesive may be cured within, e.g., several seconds toten minutes.

Third Embodiment

FIG. 8A shows a perspective view of a surface-mounted resistor 180 inaccordance with a third embodiment of the present disclosure. A basicconfiguration of the surface-mounted resistor 180 is the same as theconfiguration of the first embodiment shown in FIG. 1. A difference fromthe first embodiment is that slits 182 are provided on the lateralportions 114 of the pair of external electrodes 110. While the pair ofZ-shaped external electrodes 110 absorb and alleviate thermal impactthrough their own Z-shaped structure, the thermal impact may be furtherabsorbed and alleviated through the slits 182. Also, the slits 182 serveas relief spaces for a surplus solder possibly generated when thesubstrate connection portions 116 are soldered on the first adhesivesurface 122 a and the second adhesive surface 122 b.

The flat-type base member 102 and the pair of external electrodes 110may be fixed by using the conductive fixation materials 108 that areprovided only between the pair of internal electrodes 104 formed on theflat-type base member 102 and the internal electrode connection portions112. Alternatively, in some embodiments, the second main surface 102 b(not shown) of the flat-type base member 102 and the lateral portions114 may be fixed by using, e.g., the UV adhesive 143 shown in FIG. 7. Inthis case, the slits 182 serve as relief spaces for a surplus adhesive143 (shown in FIG. 7) that is possibly generated when the second mainsurface 102 b and the lateral surfaces 102 s of the flat-type basemember 102, and the lateral portions 114 are adhered to each other.Further, the slits 182 are configured to circulate air from inside andoutside of the space portion 110 s. This also helps maintain the spacevolume of the space portion 110 s as much as possible. The slits 182 areprovided in the thickness direction, e.g., by penetrating the lateralportions 114 from an outer side to an inner side. Alternatively, in someembodiments, without providing the slits 182, recesses and protrusionsmay be formed on at least one of outer and inner sides of at least oneof the lateral portions 114 and the substrate connection portions 116.With such configuration, it is possible to obtain the same effect as theslits 182.

FIG. 8B illustrates a modification example of the third embodiment shownin FIG. 8A. A difference from the example of the third embodiment shownin FIG. 8A is that the slits 182 are provided on both the lateralportions 114 and the substrate connection portions 116. In thisconfiguration where the slits 182 are also provided on the substrateconnection portions 116, the slits 182 serve as relief spaces for thesurplus solder that is possibly generated when the substrate connectionportions 116 are soldered on the first adhesive surface 122 a and thesecond adhesive surface 122 b, Further, the slits 182 are configured toalleviate thermal impact between the substrate connection portions 116and the first and second adhesive surfaces 112 a and 122 b. Although theslits 182 are shown on both the lateral portions 114 and the substrateconnection portions 116 in FIG. 8B, in some embodiments, the slits 182may be provided on at least one of the lateral portions 114 and thesubstrate connection portions 116.

Fourth Embodiment

FIG. 9 shows a perspective view of a fourth embodiment in accordancewith the present disclosure. A major difference from the first to thirdembodiments is a structure of an external electrode. The otherconfiguration of the fourth embodiment is almost the same as theconfiguration of the first or second embodiment.

As shown in FIG. 9, a surface-mounted resistor 200 includes a flat-typebase member 202, a pair of internal electrodes 204, a resistance element206, a protective layer 207, conductive connection materials 208, and apair of external electrodes 210. The resistance element 206 is disposedunder the protective layer 207 and is not shown in FIG. 9. The pair ofexternal electrodes 210 and the pair of internal electrodes 204 areplated with, e.g., nickel and tin (not shown).

Each of the pair of external electrodes 210 includes an internalelectrode connection portion 212, a lateral portion 214, and a substrateconnection portion 216. The external electrode 210 includes a firstbended portion 210 a having an L-shape formed by a combination of theinternal electrode connection portion 212 and the lateral portion 214,and a second bended portion 210 b having an L-shape formed by acombination of the lateral portion 214 and the substrate connectionportion 216. The lateral portion 214 includes a first lateral portion214 a and a second lateral portion 214 b.

In addition to the first bended portion 210 a and the second bendedportion 210 b, the external electrode 210 also includes a third bendedportion 210 c. The third bended portion 210 c is one of the features ofthe fourth embodiment in accordance with the present disclosure.

In addition to the first to third bended portions 210 a, 210 b, and 210c, the external electrode 210 includes the internal electrode connectionportion 212, a middle portion 224, the substrate connection portion 216,and the lateral portion 214. As described above, the lateral portion 214includes the first lateral portion 214 a and the second lateral portion214 b. The external electrode 210 of the fourth embodiment is E-shapedand is formed by a combination of two U-shaped electrodes havingdifferent sizes. This E-shaped external electrode 210 is formed byadding the middle portion 224 between the first bended portion 210 a andthe second bended portion 210 b. In the present embodiment, the E-shapedelectrode structure is formed so that the second lateral portion 214 bis horizontally shifted toward the flat-type base member 202 so that itis located closer to the flat-type base member 202 than the first laterportion 214 a. This modified E-shaped external electrode 210 isconfigured to reduce an entire mounting area by arranging the substrateconnection portion 216 mounted on a surface-mounted substrate so that itis located in proximity to the flat-type base member 202 from the firstlateral portion 214 a. In some embodiments, if the reduction of themounting area is not critical, the second lateral portion 214 b may beprovided on a co-plane with the first lateral portion 214 a. Further, anend 216 t and an end 224 t (shown in FIG. 10) may be aligned to be onthe same plane, thereby forming the external electrode 210 to have acomplete E-shape. Such complete E-shaped external electrode may also beemployed in the surface-mounted resistor in accordance with the presentdisclosure. The external electrode 210 shown in FIG. 9 may be referredto as an E-shaped external electrode in a broad sense. Further, a space(referred to as an upper spatial region) is formed between the internalelectrode connection portion 212 and the middle portion 224. In theupper spatial region, the flat-type base member 202 is disposed.Further, a space (referred to as a lower spatial region) is formedbetween the middle portion 224 and the substrate connection portion 216.The lower spatial region is used as a space portion 210 s (shown in FIG.10).

An end 224 t of the middle portion 224 is extended toward a center 206 cof the resistance element 206 over an end 202 s of the surface-mountedresistor 202. On the other hand, the end 216 t of the substrateconnection portion 216 is extended so that it does not protrude morethan the end 224 t of the middle portion 224. The end 216 t of thesubstrate connection portion 216 may be aligned on substantially thesame plane with the end 202 s of the flat-type base member 202.

The flat-type base member 202 may be attached to the pair of modifiedE-shaped external electrodes 210. The resistance element 206 is formedon the flat-type base member 202. The protective layer 207 is providedover the resistance element 206. As the protective layer 207, glass oran epoxy resin may be used. Since the resistance element 206 is coveredwith the protective layer 207, it is not shown in the perspective viewof FIG. 9. However, the positional relationship between the resistanceelement 206 and the protective layer 207 is shown in FIG. 10.

The resistance element 206 is formed as a thick film resistor having athickness of about 10 μm on a first main surface 202 a of the flat-typebase member 202 through, e.g., a screen printing. As described in thefirst embodiment, a mixture powder of, e.g., ruthenium oxide (RuO₂) andglass is used as a material of the resistance element 206. The mixturepowder is mixed with an organic binder to produce a paste. The paste isapplied on the flat-type base member 202 and baked at a temperature of800 to 900 degrees Celsius to thereby form the resistance element 206.

On both ends of the resistance element 206, the pair of internalelectrodes 204 are disposed. The internal electrode 204 is made of,e.g., silver-palladium or platinum. The internal electrode 204 is platedwith nickel and tin (not shown). The flat-type base member 202 and theresistance element 206 may be integrally formed so as not to beseparable from each other.

On both ends of a long side of the flat-type base member 202 on whichthe resistance element 206 is formed, the pair of external electrodes210 are attached. As described above, the external electrode may have amodified E-shape. This modified E-shaped external electrode 210 may havea structure with an upper spatial region and a lower spatial region(e.g., the second lateral portion 214 b defining the lower spatialregion is horizontally shifted toward the flat-type base member 202 sothat it is located closer to the flat-type base member 202 than thefirst lateral portion 214 a defining the upper spatial region, whichmakes the lower spatial region have a smaller horizontal dimension thanthe upper spatial region, as shown in FIG. 9). One feature of the fourthembodiment is that the resistance elements 206 are disposed in the upperspatial region of the pair of external electrodes 210 and the lowerspatial region thereof is used as the space portion 210 s.

In the fourth embodiment shown in FIG. 9, the flat-type base member 202is more biased toward the first bended portion 210 a in the thicknessdirection than the second bended portion 210 b as in the firstembodiment shown in FIG. 1 and FIG. 2. In other words, the flat-typebase member 202 is disposed away from the substrate connection portion216.

Both ends of the second main surface 202 b of the flat-type base member202 and a part of the middle portions 224 are fixed to each otherthrough an adhesive 242. As the adhesive 242, a UV adhesive is used, forexample. The first main surface 202 a of the flat-type base member 202with the resistance element 206 formed thereon is fixed to the internalelectrode connection portion 212 of the external electrode 210 byinterposing the conductive fixation material 208 between the internalelectrode 204 and the internal electrode connection portion 212. Also,the second main surface 202 b of the flat-type base member 202 is fixedto the middle portions 224 of the external electrode 210 by interposingthe adhesive 224 therebetween. In this way, opposing portions of theflat-type base member 202 in the thickness direction are fixed to theexternal electrode 210, such that the fixation strength thereof may beincreased.

The flat-type base member 202 is disposed in a space that is defined bya pair of U-shaped spatial regions being formed by a combination of theinternal electrode connection portions 212, the first lateral portions214 a, and the middle portions 224 which constitute the pair of externalelectrodes 210. Therefore, the fixation strength of the flat-type basemember 202 is further increased.

The space portion 210 s is formed by a pair of another U-shaped spatialregions being formed by a combination of the middle portions 224, thelateral portions 214 b, and the substrate connection portions 216. Inthis configuration, a space volume of the space portion 210 s can beadjusted as desired by controlling a height of the second lateralportion 214 b.

The internal electrode 204 and the internal electrode connection portion212 are electrically connected to each other through the conductivefixation materials 208. As the conductive fixation material 208, asolder or a silver paste may be used.

FIG. 10 illustrates a lateral cross-sectional view of thesurface-mounted resistor 200 shown in FIG. 9, showing a configuration ofthe surface-mounted resistor 200 mounted on a surface-mounted substrate.Components or portions corresponding to those shown in FIG. 9 have thesame reference numerals.

The flat-type base member 202 is made of alumina having a high purityof, e.g., 92% or 96%. The alumina has excellent mechanical strength,thermal conductivity, and insulation properties. The pair of internalelectrodes 204 are formed on the first main surface 202 a of theflat-type base member 202. The pair of internal electrodes 204 may bemade of baked silver-palladium, platinum, or the like. The resistanceelement 206 is formed on the first main surface 202 a of the flat-typebase member 202 by being partially superposed with the pair of internalelectrodes 204. As a material of the resistance element 206, a mixedmaterial of, e.g., ruthenium oxide (RuO₂) and glass, is used. Aresistance value of the resistance element 206 can be controlled bychanging a rate of mixing the ruthenium oxide (RuO₂) and the glass. Arate of containing the glass is increased to obtain a higher resistancevalue, whereas a rate of containing the ruthenium oxide (RuO₂) isincreased to obtain a lower resistance value. It is known that theruthenium oxide (RuO₂) has a resistant property against deteriorationsuch as deformation, discoloration, degradation, and the like, i.e., anexcellent weather resistant property.

The resistance element 206 is formed in a rectangular shape one side ofwhich is longer than the other side. The resistance element 206 iscovered with a protective layer (not shown). The protective layer ismade of, e.g., glass or an epoxy resin.

The external electrode 210 is fixed to the internal electrode 204 byinterposing the conductive fixation material 208 therebetween. Theconductive fixation material 208 may be a solder or a silver paste.

Each of the pair of external electrodes 210 includes the internalelectrode connection portion 212 to be fixed to each of the pair ofinternal electrodes 204 by interposing the conductive fixation material208, the lateral portion 214, the substrate connection portion 216, andthe middle portion 224, which are integrally and non-detachably formedusing the same material. The first L-shaped bended portion 210 a isformed by a combination of the lateral portion 214 and the internalelectrode connection portion 212 being positioned on an upper side ofthe external electrode 210

The second L-shaped bended portion 210 b is formed by a combination ofthe substrate connection portion 216 and the second lateral portion 214b. In addition, the third L-shaped bended portion 210 c is formed by acombination of the first lateral portion 214 a and the middle portion224.

Each of the pair of external electrodes 210 is made up with acombination of the first to third L-shaped bended portions 210 a, 210 b,and 210 c. Therefore, each of the pair of external electrodes 210 isconfigured to have an E-shape consisting of the combination of threeL-shapes.

When viewing the first lateral portion 214 a and the second lateralportion 214 b in a direction x2, the second lateral portion 214 b isdisposed closer to the end 202 s of the flat-type base member 202 thanthe first lateral portion 214 a. That is, the first lateral portion 214a and the second lateral portion 214 b are not disposed on the sameplane. This restrains the increase of a mounting area when mounting thesurface-mounted resistor 200. Specifically, if the substrate connectionportion 216 is disposed to be aligned with the first lateral portion 214a on the same plane, when the substrate connection portion 216 is fixedto the first adhesive surface 222 a or the second adhesive surface 222 bthrough a solder 218, the solder 218 may bulge from the end of theexternal electrode 210. This increases a fixation region between thesubstrate connection portion 216 and the first adhesive surface 222 a orsecond adhesive surface 222 b.

While it may increase the connection region, the external electrode 210of a complete E-shape as shown in FIG. 10 may be manufactured with abetter facility than the modified E-shape. Also, considering amanufacturing facility, the external electrode 210 may be configured toalign the end 224 t of the middle portion 224 and the end 216 t of thesubstrate connection portion 216 along the same plane. Depending on theabove requirements, the external electrode 210 in accordance with thepresent disclosure may have either the modified E-shape or the completeE-shape.

In the above, four embodiments in accordance with the present disclosurehave been described in detail. The surface-mounted resistor inaccordance with the present disclosure may be applicable to a highresistor having a high resistance value. In the high resistor, avariation of a resistance value caused by attaching the externalelectrode to the internal electrode can be neglected.

In FIG. 3B, there is shown the example where the protective layer 107 ispartially covered with the protective material 142 (142 b).Alternatively, in some embodiments, the protective layer 107 may not becovered with the protective material 142 (142 b). Further, in FIG. 3B,the protective material 142 a is not placed on the second main surface102 b of the flat-type base member 102. In some embodiments, theprotective material 142 a may be placed on the second main surface 102b. Moreover, the respective components of each of the embodiments inaccordance with the present disclosure may be properly selected andcombined in a different manner to form a novel configuration. Forexample, in the other configurations than the one shown in FIG. 3B, theconductive fixation material 108 may be covered with the protectivematerial 142.

In a similar manner as disclosed in Patent Document 7, thesurface-mounted resistor in accordance with the present disclosure maybe employed in an electric leakage detection apparatus that is mountedon, e.g., a hybrid car or an electric motor vehicle. A secondary batteryof the hybrid car or the electric motor vehicle utilizes a relativelyhigh voltage such as, e.g., 200 to 500 volt. For preventing an electricshock, such electric leakage detection apparatus employs asurface-mounted resistor having a significantly high resistance valueof, e.g., 1 to 10 Mega Ohm. For this purpose, durability against thermalimpact or mechanical vibration applied from the surface-mountedsubstrate is required rather than a flat structure.

In the surface-mounted resistor in accordance with the presentdisclosure, a height of the external electrode may be controlled so asto form a predetermined space portion between the flat-type base memberwith the resistance element formed thereon and the surface-mountedsubstrate. This may restrain damage and deterioration resulting fromstress due to thermal expansion and contraction applied from thesurface-mounted substrate. Also, even in the processing of mounting thesurface-mounted resistor, the surface-mounted substrate in accordancewith the present disclosure prevents the spread of solder wetting up tothe space portion that is formed between the flat-type base member andthe surface-mounted substrate, thereby restraining stress due to thermalexpansion and contraction applied to the resistance element.

As described above, in the surface-mounted resistor according to oneembodiment of the present disclosure, the resistance element is formedin the rectangular flat-type base member and the external electrodehaving first and second L-shaped bended portions is fixed to theinternal electrode of the resistance element. In this configuration, adistance between the first and second bended portions can be controlledto secure a sufficient space volume of the space portion. In this way,stress due to thermal expansion and contraction applied from thesurface-mounted substrate can be effectively alleviated.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications which would fall within the scopeand spirit of the inventions.

What is claimed is:
 1. A surface-mounted resistor comprising: aflat-type base member including a first main surface, a second mainsurface, and a lateral surface, each of the first main surface and thesecond main surface having a rectangular shape one side of which islonger than the other side thereof; a resistance element formed on thefirst main surface of the flat-type base member; a pair of internalelectrodes formed on both ends of the resistance element by beingpartially superposed with the resistance element; and a pair of externalelectrodes, each including a first bended portion, a second bendedportion, an internal electrode connection portion, a lateral portion,and a substrate connection portion, the first bended portion having anL-shape made up by the internal electrode connection portion and thelateral portion, and the second bended portion having an L-shape made upby the lateral portion and the substrate connection portion, wherein theinternal electrode and the internal electrode connection are fixed toeach other through a conductive fixation material, and a position of theflat-type base member is biased in a thickness direction toward thefirst bended portion.
 2. The surface-mounted resistor of claim 1,wherein each of the external electrodes is configured to have a Z-shapemade up by a combination of the first bended portion and the secondbended portion, wherein an upper portion of the Z-shaped externalelectrode corresponds to the internal electrode connection portion ofthe external electrode, a lower portion of the Z-shaped externalelectrode corresponds to the substrate connection portion of theexternal electrode, a connection portion for connecting the upperportion of the Z-shaped external electrode to the lower portion thereofcorresponds to the lateral portion of the external electrode, and thesubstrate connection portion is configured to protrude away from an endof the longer side of the flat-type base member.
 3. The surface-mountedresistor of claim 1, wherein the flat-type base member is suspended fromthe internal electrode connection portion by interposing the conductivefixation material between the flat-type base member and the internalelectrode connection portion.
 4. The surface-mounted resistor of claim1, wherein the flat-type base member is placed on the internal electrodeconnection portion by interposing the conductive fixation materialbetween the flat-type base member and the internal electrode connectionportion.
 5. The surface-mounted resistor of claim 1, wherein an area ofthe external electrode facing the internal electrode is set to begreater than an area of the external electrode facing the lateralsurface of the flat-type base member.
 6. The surface-mounted resistor ofclaim 1, wherein a space volume ratio Va is defined by the followingequation: Va=H4/H1, wherein H1 is a height from the second bendedportion to the first bended portion and H4 is a height from the secondbended portion to the second main surface of the flat-type base member,and wherein the space volume ratio Va is in the range of 0.3 to 0.9. 7.The surface-mounted resistor of claim 1, wherein a space volume ratio Vais defined by the following equation: Va=H4/H1, wherein H1 is a heightfrom the second bended portion to the first bended portion and H4 is aheight from the second bended portion to the second main surface of theflat-type base member, and wherein the space volume ratio Va is in therange of 0.5 to 0.8.
 8. The surface-mounted resistor of claim 1, whereina predetermined space is provided between the second main surface of theflat-type base member and the substrate connection portion in thethickness direction of the flat-type base member.
 9. The surface-mountedresistor of claim 1, wherein a distance between the pair of internalelectrodes is 5.2 mm or greater.
 10. The surface-mounted resistor ofclaim 1, wherein a gap is provided between the lateral portion and theend of the longer side of the flat-type base member.
 11. Thesurface-mounted resistor of claim 1, wherein a part of the lateralportion and the second main surface of the flat-type base member arefixed to each other through an adhesive.
 12. The surface-mountedresistor of claim 1, wherein the external electrode is configured tohave an E-shape including an upper region and a lower region, which arespatially divided by a middle portion being provided between the firstbended portion and the second bended portion, wherein the flat-type basemember is disposed in the upper region of the E-shaped externalelectrode, and the lower region of the E-shaped external electrodedefines a space portion.
 13. The surface-mounted resistor of claim 1,wherein a slit is provided on at least one of the lateral portion andthe substrate connection portion, the slit penetrating at least one ofthe lateral portion and the substrate connection portion in a thicknessdirection.
 14. The surface-mounted resistor of claim 1, wherein recessesand protrusions are provided on at least one of the lateral portion andthe substrate connection portion in a thickness direction.
 15. Thesurface-mounted resistor of claim 12, wherein a part of the second mainsurface of the flat-type base member and a part of the middle portionare fixed to each other through an adhesive.
 16. The surface-mountedresistor of claim 1, wherein a resistance value of the surface-mountedresistor is 1 Mega Ohm or more.
 17. An electric motor vehicle comprisingthe surface-mounted resistor of claim
 16. 18. A surface-mountedsubstrate for mounting the surface-mounted resistor according to claim1, the surface-mounted substrate comprising, a first adhesive surfaceand a second adhesive surface configured to be connected to both ends ofthe surface-mounted resistor, respectively, wherein a shortest distancebetween the pair of lateral portions of the surface-mounted resistor isless than a shortest distance between an end of the first adhesivesurface and an end of the second adhesive surface facing the end of thefirst adhesive surface.
 19. The surface-mounted resistor of claim 1,wherein a surface of the conductive fixation material is covered with aprotective material.
 20. The surface-mounted resistor of claim 19,wherein the protective material is made of an insulation resin.